Ewing sarcoma among children 5 years of age or younger: Is it a different disease?

Introduction: Children <= 5 years of age with Ewing's sarcoma (ES) possibly have a distinct disease biology, data on which are scarce. We evaluated clinical features, outcomes, and prognostic factors of ES among children with age <= 5 years. Methods: Children with ES registered between 2003 and 2019 were included. Baseline clinical and treatment details were retrieved from medical records. Prognostic factors were identified using multivariable Cox regression. Clinical features and outcomes of children <= 5 years were compared with those greater than 5 years by chi-square and log-rank tests. Propensity score-matched (PSM) analysis was done to evaluate the impact of age on survival in the metastatic and localized subgroups. Results: Out of the 859 patients, 86 (10%) were <= 5 years of age (median age 4 years, 60 males [69.8%]). The most common location was the extremities (37.2%), followed by thorax (27.9%) and head and neck (H&N) (22.1%); baseline metastases were seen in 25 patients (29.8%). The median event-free-survival (EFS) and overall survival (OS) were 25.6 and 68.7 months, respectively. Metastatic disease predicted inferior OS (hazard ratio [HR] = 2.54, p = .018) and EFS (HR = 2.47, p = .007], symptom duration <= 3 months predicted an inferior OS (HR = 2.17, p = .048). Compared to age greater than 5 years, younger children had more H&N and less pelvic primaries (p < .001) and lesser baseline metastases (p = .037). PSM analysis did not reveal any significant impact of age on OS in the metastatic (HR = 1.59, p = .29) or localized cohort (HR = 1.77, p = .09). Conclusions: Children with ES <= 5 years of age have a distinct favorable clinical presentation. However, age is not an independent prognostic factor for survival outcomes when adjusted for confounders.